Powerful storms swept through parts of Northern California on Saturday, knocking down trees, causing widespread power outages and prompting weather officials to issue what they said was the first-ever tornado warning for San Francisco.

San Francisco residents were woken up by a tornado warning early Saturday morning during a powerful storm system that battered the region with heavy rain and wind.

A potent winter storm targeting Northern California this weekend brought what appears to be the first official tornado warning on record for the city of San Francisco on Saturday morning.